Composition and process for cross-linking macromolecular polysaccharide solutions

ABSTRACT

A CROSS-LINKING AGENT FOR MACROMOLECULAR POLYSACCHARIDE MATERIALS CONSISTING ESSENTIALLY OF A CHELATING COMPOSITION FORMED FROM (1) AN ORGANIC POLYELECTROLYTE LIGAND COMPONENT, AND (2) A COMPONENT OF A METAL OF THE FIRST SERIES OF THE TRANSITION ELEMENTS OF THE PERIODIC TABLE. THIS CROSS-LINKING AGENT HAS BEEN FOUND TO PROVIDE ENHANCED RHEOLOGICAL PROPERTIES WITHOUT OBTAINING METAL ION OVERTREATMENT CHARACTERISTICS. IN A PREFERRED FORM, SAID CROSS-LINKING AGENT ALSO INCLUDES A COMPOUND CONTAINING A METAL FROM GROUP II OF THE PERIODIC TABLE. THE CROSS-LINKED MATERIALS MAY BE UTILIZED IN TEXTILE SIZING AGENTS, PAINTS, DRILLING FLUIDS, AND THE LIKE.

May 14, 1974 w c BROWNlNG ETAL 3,810,882

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NNVdo ay 14, 1974 w c, BROWNlNG ETAL 3,810,882

COMPOSITION AND PROCESS FOR CROSS-LINKING MACROMOLECULAR POLYSACCHARIDE SOLUTIONS Original Filed June 18, 1970 6 Sheets-Sheet 5' Lu m May 14, 1974 553mm 8 Q 8 m w v N o E U 354a MEQKIU 6 Sheets-Sheet 6 kzmw @225 4 wwOtu W. C. BROWNING ETAL COMPOSITION AND PROCESS FOR CROSS-LINKING MACROMOLECULAR POLYSACCHARIDE SOLUTIONS Original Filed June 18, 1970 WdH O09 .LV NNVJQ 06 I m mqruuqmbom fi E22 2m 22833 E mzofiiom mmEqrSqwfiom zo fizfiufim 23 5 mzomzu nzq Em? @2254 $05 mo zomiqmzou I United States Patent 3,810,882 COMPOSITION AND PROCESS FOR CROSS-LINK- ING MACROMOLECULAR POLYSACCHARIDE SOLUTIONS William C. Browning and Billy G. Chesser, Houston, Tex., assignors to Milchem Incorporated, Houston, Tex. Original application June 18, 1970, Ser. No. 47,325, now Patent No. 3,697,498. Divided and this application Aug. 21, 1972, Ser. No. 282,376

Int. Cl. C07c 3/00 US. Cl. 260-209 R 4 Claims ABSTRACT OF THE DISCLOSURE A cross-linking agent for macromolecular polysaccharide materials consisting essentially of a chelating composition formed from (1) an organic polyelectrolyte ligand component, and (2) a component of a metal of the first series of the transition elements of the Periodic Table. This cross-linking agent has been found to provide enhanced rheological properties without obtaining metal ion overtreatment characteristics. In a preferred form, said cross-linking agent also includes a compound containing a metal from Group II of the Periodic Table. The cross-linked materials may be utilized in textile sizing agents, paints, drilling fluids, and the like.

CROSS REFERENCE TO RELATED APPLICATIONS This is a division of application Ser. No. 47,325, filed June 18, 1970, now Pat. No. 3,697,498.

BACKGROUND OF THE INVENTION (1) Field of the invention-This invention relates to a novel cross-linking agent for macromolecular polysaccharide materials. These materials are readily soluble in water and form enhanced shear rate thinning viscoelastic solutions when cross-linked with the cross-linking agent of the present invention. Solutions of these substances therefore characteristically exhibit a decrease in apparent viscosity as shear rate is increased and an increase in apparent viscosity as the rate of shear is decreased. These non-Newtonian solutions are generally temperature stable up to about 250 F., and are generally functional in solutions of inorganics electrolytes.

(2) Descriptio of the prior art-In the past, those skilled in the art have relied heavily upon water soluble salts of polyvalent metal cations from Group HI through Group VIII of the Periodic Table, such as chromium, to provide cross-linking of macromolecular polysaccharide materials in order to enhance their thixotropic, shear thinning characteristics. Chromic salt-containing compounds, such as chromium chloride, basic chromium sulfate, chromium aluminum sulfate, and the like have been particularly utilized. However, the successful use of these materials alone has been somewhat limited because of a metal ion overtreatment effect on the macromolecular polysaccharide material. For example, chromium chloride and chrome alum have been found to overtreat the macromolecular polysaccharide material, i.e., when the cross-linking agent has been added in a concentration excess of about 0.5 p.p.b. (lb./mml.), this lowering of apparent viscosity due to overtreatment will occur and will cause the solution to be thinned rather than thickened. Therefore, increased levels of the usual metal salt cross-linking agent can produce an effect opposite of what was intended.

There is, therefore, industrial and commercial need of a material which will effectively cross-link macromolecular polysaccharide materials to provide a mechanically and chemically stable cross-linked macromolecular polysaccharide material not exhibiting this overtreatment cf- 3,810,882 Patented May 14, 1974 feet. We have found that certain organic polyelectrolyte ligands may be reacted with certain compounds containing a metal from the first series of the transition elements of the Periodic Table to form a chelating composition which will act as cross-linking agents for certain macromolecular polysaccharide solutions. These organic chelates do not exhibit the overtreatment effect characteristic of inorganic metal salts of the elements present in Group III through Group VIII of the Periodic Table.

It is an object of the present invention to provide a new cross-linking agent for macromolecular polysaccharide materials used in aqueous solutions in which an organic polyelectrolyte is believed to act as the ligand for a transition element metal effective as a cross-linking agent.

It is also an object of the present invention to provide organic polyelectrolyte ligands to treat aqueous macromolecular polysaccharide solutions to produce a positive and controlled thickening eifect, without any undesired overtreatment or thinning effects.

It is also an object of the present invention to prevent metal ion overtreatment of macromolecular polysaccharide materials resulting in a decrease in solution viscosity.

It is a further object of the present invention to provide a method of drilling subterranean wells utilizing the cross-linking agent of the present invention.

Other objects and advantages of the use of the present invention will be readily appreciated from a reading of the description of the invention, the drawings, the examples, and the claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphical illustration comparing the room temperature viscosities of a solution of macromolecular polysaccharide material with and Without the cross-linking agent of the present invention.

FIG. 2 is a graphical illustration comparing room temperature viscosities of a solution of a macromolecular polysaccharide material cross-linked with a one-third basicity chrome sulfate and a duplicate macromolecular polysaccharide sample cross-linked with the cross-linking agent of the present invention.

FIG. 3 is a rheogram comparing the room temperature viscosities of a 1 p.p.b. solution of a macromolecular polysaccharide material cross-linked with the cross-linking agent of the present invention and a ferrochrome lignosulfonate compound, respectively.

FIG. 4 is a graphical illustration of the non-overtreating characteristic of the cross-linking agent of the present invention.

FIG. 5 is a rheogram showing the elimination of metal ion overtreatment effect on a macromolecular polysaccharide solution using 6 p.p.b. of the cross-linking agent of the present invention and 1 p.p.b. macromolecular polysaccharide material.

FIG. 6 is a graphical illustration of the room temperature apparent viscosity of macromolecular polysaccharide solutions cross-linked with the cross-linking agent of the present invention compared with the effect obtained by the use of chrome alum, in Galveston Bay water. The desirable controlled, positive cross-linking obtained with our cross-linking agent is strikingly apparent.

SUMMARY OF THE INVENTION The present invention comprises a cross-linking agent for macromolecular polysaccharide materials consisting essentially of a chelating composition formed from (1) an organic polyelectrolyte ligand component and (2) a component of a metal of the first series of the transition elements of the Periodic Table. It is presently preferred that a compound containing a metal element from Group II of the Periodic Table be further incorporated in the composition of said cross-linking agent. The cross-linking agent may be utilized with macromolecular polysaccharide materials such as biologically polymerized glu cose, corn starch, potato starch, soluble starches, chemically modified starch, and polysaccharides produced by the action of bacteria such as the genus Xanthomonas on carbohydrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS When discussing macromolecular polysaccharide materials, we mean to refer to the use of polysaccharides or gums technically employed in industry. These organic materials are dispersible in either cold or hot water to produce viscous mixtures or solutions. Of particular interest are exudate gums, seaweed gums, seed gums, and starch and cellulose derivatives. Other macromolecular polysaccharides such as dextrins and dextrans derived from corn starch, potato starch, and other soluble starches as well as polysaccharide biopolymers produced by the action of bacteria on a carbohydrate may be utilized. Our cross-linking agent is particularly effective when utilized in conjunction with macromolecular polysaccharide materials produced by bacterial action of the genus Xanthomonas on carbohydrates. These bacteria may be of the species X anthomonas begoniae, Xanthomonas campestris, Xanthomonas carotae, Xanthomonas corylina, Xanthomonas gummisudens, Xanthomonas hederae, Xanthomonas incanae, Xanthomonas lespedezae, Xanthomonas malvacearum, Xanthomonas holcicola, Xanthomonas papavericola, Xanthomonas phaseoli, Xanthomonas pz'si, Xanthomonas translucens, Xanthomonas vasculorum, Xanthomonas vesicatoria, and the like. We have found our cross-linking agent to be particularly effective in treating the macromolecular polysaccharide material produced by the action of the bacteria Xanthomonas on a carbohydrate. This macromolecular polysaccharide material may be obtained by utilizing methods such as those disclosed in U.S. Pats. Nos. 3,000,790, 3,020,206, 3,228,- 855, 3,455,786, and 3,485,719.

Our cross-linking agent may be better defined as a chelating composition. The term chelate was originally proposed to designate those cyclic structures which arise from the union of metallic atoms with organic and inorganic molecules or ions. If a molecule is to function as a chelating agent, it must fulfill at least two conditions. First, it must possess two appropriate functional groups, the donor atoms of which are capable of combining with a metal atom by donating a pair of electrons. These electrons may be contributed by basic coordinating groups such as NH or acidic groups that have lost a proton. Second, these functional groups must be so situated in the molecule that they permit the formation of a ring with the metal atom as the closing member. The donor group is termed a ligand and the metal atom the acceptor.

Chelates can only be formed by ligands that have more than one point of attachment to the metal. Therefore, a bidentate or polydentate ligand can form a chelate, but an unidentate ligand cannot form a chelate. Thus, for example, an unidentate sulfonic acid salt is not by definition a chelate.

Organic polyelectrolyte ligands containing reactive groups capable of forming metal chelates may be used as ligands in our cross-linking agent. For example, lignincontaining materials such as kraft lignin, soda lignin, polyphenolic tannins and polyfiavonoids may function as suitable ligands. Lignosulfonates in which the sulfonic groups have been prereacted and saturated with sodium or ammonium ions are especially useful as ligands for the preparation of the cross-linking agent of this invention. Lignin-containing materials as used in the practice of this invention are readily available as by-products of chemical processes making chemical wood pulp or wood cellulose which are used to make paper and other products. The three processes generally used to chemically extract the cellulose from the wood, leaving the lignin from the wood in the waste liquor, are the soda process, the sulfate process, and the bisulfite or sulfite process. In general, any type of wood or lignocellulosic material which can be resolved into cellulose pulp by one of these three processes may be used as a source of lignin-containing materials for use in accordance with our discovery.

For reasons of economy, we prefer to utilize a sulfonated lignin-derived polymer which can be prepared by cooking wood chips with a sodium bisulfite or by adding sodium salts to calcium sulfite waste liquor in a manner calculated to cause a precipitation of the calcium ion and thereby forming the sodium salt of lignosulfonic acid. A sulfonate lignin-derived polymer derived from basic calcium lignosulfonate made in accordance with the procedures disclosed in patents such as United States Reissue Patent Nos. 18,268 and 18,369 may be used. The calcium lignosulfonate is converted to the sodium salt by reaction of the sulfonic groups of the lignosulfonate with stoichiometric equivalent amounts of sodium salts, the anions of which will form water insoluble calcium salts, such as sodium phosphate, sodium fluoride, sodium oxalate, and sodium carbonate. Other metallic salts of lignosulfonates may also be used.

Although preferred, it is not essential in the preparation of the cross-linking agent of the present invention that sulfonated lignin-containing materials be used, for it has been found that practically any material containing reactive groups capable of forming metal chelates can be used to form the cross-linking agent of the present invention.

Moreover, natural tannin-containing polyelectrolytes such as Wattle extract or Quebracho may also be used as the ligand in the cross-linking agent of the present invention. Bark extracts derived by bisulfite cooking of hemlock, redwood, douglas fir, and similar barks, may also be used. The teachings of patents such as U.S. Pat. Nos. 2,890,231 and 2,938,893 or similar known processes may be used to obtain a satisfactory bark extract as the organic polyelectrolyte ligand component for use in our cross-linking agent.

When using a lignosulfonate as the ligand material, we prefer to utilize a lignosulfonate which is essentially free of wood sugars and hemicellulose. For example, when reacting spent sulfite liquor with materials such as sulfuric acid and sodium sulfate in a water solvent system to provide sodium lignosulfonate, it is desirable to destroy the residual sugar content with ammonia gas, heat, or other additives or processes known to those skilled in the art.

In order to achieve enhanced characteristics the lignin polyelectrolyte ligand material should be polymerized to such a degree that the resulting product in an aqueous solution has a viscosity of about centipoises at 30 C. with 36% by weight solids. Polymerization may be practiced by any suitable effective method known to those skilled in the art. However, we have found that excellent lignin polymer characteristics may be obtained by utilizing formaldehyde condensation polymerization tech niques.

Our cross-linking agent also contains a compound containing a metal from the first series of the transition elements. The transition elements may be defined as those elements which have partly filled d or f shells in any of their commonly occurring oxidation states. The first series transition elements includes scandium, titanium, vanadium, manganese, iron, cobalt, chromium, nickel, and copper.

When chromium has been selected as the metal component from the first series of transition elements, our tests have indicated that not all chromium salts react suitably with the organic polyelectrolyte ligand component. We have found that it is essential that the chromium not be introduced in the organic polyelectrolyte ligand cornponent by an oxidation reaction as by reacting with ehromates or dichromates, for this causes the chromium to be covalently bonded in the organic molecule in such a manner as to render the chromium unavailable for base exchange or for cross-linking reactions. We have further found that there are even great differences in, for example, nominal chrome sulfates and that, when using a chrome sulfate, it is imperative that chrome sulfates having specific properties be utilized. We have found, when selecting chrome in the form of chrome sulfate as the transition metal component, that a chrome sulfate compound having properties within the following ranges will be effective in producing the cross-linking agent of the present invention without metal ion overtreatment effects:

Properties: Effective range Basicity, degrees Schlorlemmer 33 /3 to 0 pH, solution 2.3 or less Wt. percent solution basis:

Total chrome 12.5 to 11.8 Total sodium 6.0 to 5.0 Total sulfate sulfur 16.0 to 15.0 Total solids 66 to 60.0

We prefer to utilize a chrome sulfate product with the following properties:

Properties: Eflfective range Basicity, degrees Schlorlemmer 13 /3 pH, solution 22.0

Wt. percent solution basis:

Total chrome 12.1 Total sodium 5.8 Total sulfate sulfur 15.2 Total solids 65.0

Assuming that the chrome sulfate is prepared by the reduction of sodium dichromate by a reducing agent in a sulfuric acid solution, the basicity of the resulting chromium sulfate compound may be determined as follows:

When using chrome sulfate in obtaining the cross-linkin-g agent of the present invention it is imperative that the basicity of the chrome sulfate be one-third or less and that a chrome sulfate having the above described properties be used. Stating that a basic chrome sulfate may be utilized is not definitive enough to determine the particular chrome material that must be used in accordance with the invention.

Although not fully understood, it is believed that the effective cross-linking of the macromolecular polysaccharide material with the agent of the present invention is obtained due to the ability of certain organic polyelectholyte ligands to form chelates of controlled stability coefiicient with a component containing a metal of the first series of the transition elements of the Periodic Table, such as chromium. For example, chromium chelates make the metal available for the cross-linking of the hydroxyl groups of the macromolecular polysaccharide material in a controlled or buffered manner that prevents chromium ion overtreatment effects and minimizes other undesirable side reactions of the chromium ions that may occur through dissociation of ordinary chrome sulfates, chlo-' rides or alums.

We have found that the effectiveness of the cross-linking action of our chelate composition with macromolecular polysaccharide materials is enhanced by the addition into the organic polyelectrolyte ligand of a compound containing an element from Group II of the Periodic Table. For example, the incorporation of magnesium into the organic polyelectrolyte ligand component greatly increases the commercial utility of the compound by increasing its effectiveness in a variety of natural waters. When selecting magnesium, we have found that about 3.5% by weight, dry solids basis, to the entire composition, is a sufficient amount under normal circumstances to produce effective cross-linking. We have also found that this material may be effectively introduced in the reaction process as magnesium chloride. When utilizing magnesium chloride we prefer to add about 13.72% by weight on an anhydrous basis based on the weight of the entire composition.

When reacting chrome sulfate as above described with the organic polyelectrolyte ligand, we prefer to use about 5.7% chromium by weight of the entire cross-linking agent composition, although the chromium content may be as low as 4.0% and as high os 10.0%. The chrome sulfate is added to the solution in a reaction vessel and agitation is initiated and continued for at least 30 minutes in order to assure complete reaction. The resulting material may be utilized in liquid, or spray dried and used in powder form.

The actual cross-linking of the macromolecular polysaccharide material with the cross-linking agent of the present invention may be effected in one of several ways which will provide a solution with enhanced rheological characteristics. For example, when utilizing the macro molecular polysaccharide material in an aqueous drilling fluid, the macromolecular polysaccharide material and the cross-linking agent of the present invention may be added simultaneously to the water circulating in the well. Preferably, the macromolecular polysaccharide material is dispersed and circulated in the water solution followed by the addition of the cross-linking agent of the present invention. Cross-linking of the macromolecular polysaccharide material may also take place in a convenient mixing tank adjacent to the well site.

The amount of cross-linking agent of this invention which may be utilized with the macromolecular polysaccharide material is not critical and will vary depending upon the particular application at hand. Any amount suflicient to produce cross-linking may be added. We have found that metal ion overtreatment characteristics will not result when using our cross-linking agent in cross-linking agent-to-polysaccharide ratios as low as l-to-l and as high as 24-to-l. When using a cross-linked macromolecular polysaccharide solution in an aqueous drilling fluid, a 4-to- 1 polysaccharide-to-cross-linking agent ratio should be sufficient to produce the desired controlled rheological properties. It is important to note that these solutions are distinct due to the fact that no bentonite or similar agent is added or desired for the system to function effectively.

After the addition of the cross-linking agent, the pH of the solution should be adjusted to a range between about 6 and about 7 with sodium hydroxide or a similar chemical. We have found that a pH adjustment to about 7 is quite satisfactory. The solution should be mechanically stirred in order to prevent a localized high pH condition. After initial mixing, the pH of the aqueous solution may be adjusted up to about 11.0.

In order to prevent biodegradation, a common occurrence in macromolecular polysaccharide materials, a biocide or biodegradation preventative such as Dowcide G, manufactured by The Dow Chemical Co., should be added shortly after initial pH adjustment. Other known additives, such as paraformaldehyde, may also be used. We prefer to add about 0.1 p.p.b. to 0.5 p.p.b. of this chemicaldissolved in water to the cross-linked polysaccharide solution.

The cross-linked macromolecular polysaccharide solutions are valuable for a diversity of industrial uses, e.g., textile printing pastes, latex dispersions, coating materials, as a protective colloid for pre-emulsions, and as a textile sizing and finishing agent. They have also been found to be an important constituent of aqueous drilling fluids.

The invention is further described and illustrated by the examples that follow. The chrome alum utilized throughout the examples and in the attached figures has the formula Cr (SO )3K SO .24H O. This material is available as Baker and Adamson chromium potassium sulfate and is manufactured by Allied Chemical Co., General Chemical Division, Morristown, N]. This material is readily available to the general public.

The macromolecular polysaccharide material, also referred to as simply polysaccharide," utilized in the examples and figures is the product of the fermentation reaction of the bacteria Xanthomonas campestris on carbohydrates. This material is commercially available as Kelzan )cligolymer, made by Kelco Corporation of San Diego,

EXAMPLE I The present example demonstrates a preferred process for obtaining the cross-linking agent of the present invention. Thirteen thousand five hundred (13,500) kg. of sodium lignosulfonate liquor of about 38% solids having present no more than about 7% sugar content is pumped to a drum reactor. The pH of the sodium lignosulfonate liquor to obtain a pH to about 7.5 and to adequately destroy the sugar content of the sodium lignosulfonate. After pH adjustment, the temperature of the reactor is raised to about 130 C. This process is continued for about 120 minutes.

Polymerization is initiated by injecting a solution of 2% formaldehyde in the circulation line while circulating the liquor. Upon the conclusion of formaldehyde injection, the temperature of the reaction mixture is maintained at 130 C. for an additional 45 minutes. The reactants are then cooled down to 70-80 C.

A 33% solution of magnesium chloride (340 liters) is slowly added to five hundred fifty-one (551) kg. of the desugared and polymerized sodium lignosulfonate solution. Two hundred seventy (270) liters of the preferred chrome sulfate solution is slowly injected into the liquor circulation line. After the complete addition of the preferred chrome sulfate with the lignosulfonate, the mixture is agitated for about 30 minutes to insure complete reaction. The cross-linking agent is then spray dried.

EXAMPLE II The present example demonstrates the ability of the cross-linking agent of the present invention to effectively cross-link macromolecular polysaccharide materials.

A sample of a solution of the cross-linking agent prepared as in Example I was cross-linked with a macromolecular polysaccharide material and was compared with an untreated sample of the macromolecular polysaccharide material. The cross-linking agent was utilized with the macromolecular polysaccharide material in a ratio of 12 lb./bbl. of cross-linking agent to one lb./bbl. macromolecular polysaccharide material. The untreated sample containing only the macromolecular polysaccharide material was prepared at the one lb./bbl. level. The Water utilized was treated to simulate natural water in that all samples were contaminated with 100 p.p.m. calcium ion. The pH was then adjusted to 8.5 with sodium hydroxide after crosslinking. Viscosity data was determined at room temperature by utilizing a Model 35 Fan Viscometer, a common instrument for measuring rheological properties of liquids, widely accepted by many industries where rheological data is relevant. Fann viscometers are of the concentric cylinder type where the test fluid is contained in an annular space between cylinders. Rotation of the outer cylinder at known velocities is accomplished through precision gearing causing a torque to be transmitted to the inner cylinder by the viscous drag of the fluid. This torque is balanced by a 8 helical spring, and angular deflection is read from a dial or through suitable sensors on a meter or recorder. The amount of torque at a given r.p.m. is indicated in arbitrary degrees Faun, which may be converted into viscosity or apparent viscosity by appropriate calculation. The apparent viscosity of non-Newtonian fluids or viscosity of Newtonian fluids may be obtained from the Faun reading as follows: Viscosity in centipoises Approximate apparent viscosity of:

1. Degrees Faun at 600 r.p.m. /2

2. Degrees Fann at 300 r.p.m. 1

3. Degrees Faun at 200 r.p.m. 1%

4. Degrees Fann at r.p.m. 3

5. Degrees Fann at 6 r.p.m. 39

6. Degrees Faun at 3 r.p.m.X98

The results of these tests, shown in FIG. 1, indicated that the cross-linking agent of the present invention effectively cross-linked with the macromolecular polysaccharide material to produce a shear rate thinning solution. The table below further indicates the results of these tests.

TABLE 2 Untreated polysaccharlde material I Cross-linking agent I Apparent Apparent viscosity, viscosity, Faun cps. Faun cps.

B..p.m

15. 0 7. 5 39. 0 19. 5 11. 0 11. 0 27. 0 27. 0 10. 0 15. 0 21. 0 31. 5 8. 0 24. 0 16. 0 48. 0 6 3. 0 147. 0 8.0 392. 0 3 3. 0 294. 0 7. 0 616. 0 Initial gel, 1b./l00 s 3. 0 11. 0 p 9. 5 8. 8 NaOH used to adjust pH, cc- 0. 1 4. 8

I All tests determined at room temperature.

EXAMPLE III Tests were run in order to compare results of crosslinking macro-molecular polysaccharide materials with a chrome sulfate having above described properties with and without the cross-linking agent of the present invention, respectively. Gypsum was added to ordinary Houston, Texas, tap water to obtain the equivalent of 100 p.p.m. calcium ion content. One p.p.b. equivalent of the macromolecular polysaccharide material was added to 350 ml. of the water and blended by mechanical agitation. The chrome sulfate and the cross-linking agent of the present invention made as in Example I were then added to the respective samples. Various p.p.b. levels of crosslinking agents were utilized. The pH of the solutions was adjusted to 8.5 with sodium hydroxide in order to obtain maximum cross-linking. The samples were allowed to age overnight before rheological data was obtained using the Fann Viscometer as previously described. FIG. 2 graphically depicts the results of this test.

As can be seen in the table below, the cross-linking agent of the present invention provided a more stable thickening agent with increased thickening characteristics as increased p.p.b. levels of the agent were utilized. It will also be seen that th problem of overtreatment has been drastically reduced through the use of the crosslinking agent of the present invention.

1 1 EXAMPLE v Tests were run and results evaluated in order to determine the ability of the cross-linking agent of the present invention to prevent chromium ion overtreatment of macromolecular polysaccharide materials. The tests were conducted in hard water contaminated with 100 p.p.m. calcium ion. One p.p.b. of the polysaccharide material was utilized with p.p.b. levels from to 10 of a basic chromecontaining, cross-linking compound, chrome alum, and the cross-linking agent of the present invention made according to Example I, respectively. The pH of the solutions was raised with sodium hydroxide to 9.0. The Fann viscometer, as described above, was again utilized to obtain rheological data. The Faun readings were taken at the 600 r.p.m. level at room temperature. FIG. 4 illustrates the results of this test. As can be seen, the cross-linking agent of the present invention produced a thinning of the polysaccharide material after a peak in thickening at the 1 p.p.b. level. This characteristic is called overtreatment and, as can also be seen, was completely eliminated by the use of the cross-linking agent of the present invention. The results of this test are described in detail in the following table.

TABLE Cross-linking agent l 2 EXAMPLE v1 Calcium content mg./ml 0.170 Magnesium content mg./ml 0.460 Sodium content mg./ml 3.8 Sulfate content mg./ml 9.83 Chloride content mg./ml 6.8 Specific gravity mg./ml 1.009 pH 7.4

The test samples were prepared by adding to 350 ml. samples of the water one p.p.b. equivalent of the macromolecular polysaccharide material. Blending was achieved by mechanical agitation. The samples were then treated with 0, 1, 2, 4, 6, 8 and 10 p.p.b., respectively, of the P.p.b.: Fann at 600 r.p.m.

0 15 cross-linking agent of the present invention, made as in 1 30 Example I. Other samples of the macromolecular poly- 2 34 saccharide material were treated with chrome alum at 4 0.10, 0.25, 0.50, 1.50, 3.00, 5.00 and 10.00 p.p.b. levels, 6 8 40 respectlvely, and also blended by mechanlcal agltatlon. 10 47 The pH of all samples was then raised to 9.0 with sodium Chr 1 m 35 hydroxide. All samples were allowed to cool to room tem mm a u peratures before Fann readings were initiated. P.p.b.: Farm at 600 '-P- Table 6-A below contains the results of tests using the chrome alum compound while Table 6-B below illustrates 2 19 40 the results obtained with the cross-linking agent of the 4 u 11 present invention. It is of special interest to note that 6 9 chrome alum gave poor results at all concentrations eval- 3 9 uated. Maximum cross-linking was obtained with 0.10 10 9 p.p.b. of the chrome alum sample.

TABLE 6-A Chrome alum, p.p.b.

F/R A/V FIR A/V F/R A/V F/R A V F/RI A/V F/R A/V F/R A/V F/R A/V 49 24.5 28 14 12 5 11.5 5.75 8 4 8 4 7 3.5 7 3.5 35 35 18 18 7 7 7 7 5 5 5 5 4 4 4 4 29 43.4 15 22.5 5 7.5 5 7.5 3 4.5 3 4.5 3 4.5 3 4.5 22 10 30 4 12 3 9 2 5 2 5 2 5 2 5 9 441 4 195 1 49 1 49 0 0 0 0 0 0 0 0 3- 8 754 3 294 1 98 1 98 00 0 0 0 0 0 0 0 Initial gel, lb./100 sq.

ft, 12 5 2 2 2 2 1 1 pH 9.2 9.2 9.0 90 90 9.0 90 90 l Faun reading, Fann. I Apparent viscosity.

TABLE 5-13 Cross-linking agent of the present invention, p.p.b.

F/R A/V F/R A/V' F/R 2N F/R A V F/R A/V' F/R A/V F/R AN 49 24.5 52 25 50 25 50 25 55 27.5 55 27.5 57 28.5 35 35 38 38 35 35 35 35 40 40 40 40 42 42 29 43 5 31 45.5 30 45 30 45 35 52.5 35 52 5 35 52.5 22 55 23 59 22 55 21 53 25 25 75 25 75 9 441 8 392 8 392 8 392 11 533 10 490 12 588 3 8 784 7 686 7 585 7 585 10 980 9 882 11 1,078 Initial gel, lb./100 sq. ft 12 12 12 11 13 10 pH 9.2 9.0 9.0 9.0 9.0 00

1 Farm reading, Faun. I Apparent viscosity.

13 EXAMPLE VII Tests were run, as in Example VI above, except that a brine system replaced the Galveston Bay seawater. Brines are often encountered in the actual drilling of oil and gas wells and are a difficult environment in which to crosslink a macromolecular polysaccharide material and to control drilling fiuid rheology.

The synthetic brine samples were prepared by dissolving 82 grams of CaCl -2H O in 350 m1. of deionized water. Reagent grade calcium chloride was utilized. Samples, as made in Example VI above, were again prepared and evaluated. Tables 7-A and 7-B illustrate the results of this test. It should be noted that only at the 0.10 p.p.b. concentration did chrome alum obtain a satisfactory crosslinking effect.

in both calcium-contaminated Houston, Tex., tap water,

i.e., hard water, and synthetic seawater. The hard water.

was prepared for the samples by placing 1'00 p.p.m. calcium as calcium sulfate in 350 ml. deionized water. The synthetic seawater was prepared by adding to 350 ml. deionized water 400 p.p.m. calcium as calcium sulfate and 30,000 p.p.m. chloride as sodium chloride.

Samples containing 100 p.p.m. hard water and synthetic seawater, respectively, were treated with 0.50 and 0.75

10 p.p.b. of the macromolecular polysaccharide material and were then blended by mechanical agitation. The samples were then treated with 2, 6, and 12 p.p.b., respectively, of the cross-linking agent made as in Example I, and were again mechanically agitated. The pH of each sample was 15 adjusted to 9.0. The samples were cooled to room tem- TABLE 7A Chrome alum, p.p.b.

F/R AN 9 F/R A/V F/R 1 AN F/R A/V F/R A/V l F/R A/V FIR 1 A/V F/R l AIV 18. 5 9. 25 33 46. 5 37 18. 5 17 8. 5 13 6. 5 7. 5 18 9 14 7 13. 5 13. 5 23 23 25 25 10 10 8 8 10 10 8 8 9 9 11.5 17. 5 18 27 30 7 10. 5 5 7. 5 7 10. 5 5 9 7 10. 5 8 24 14 42 14 42 5 15 3 9 4 12 4 12 5 15 2 98 5 5 269. 5 5 245 1 49 0 0 1 49 1 49 l 49 3 1. 5 147 5 O 490 4 392 0 0 0 0 0 0 1 98 1 98 Initial gel, lb./l00

sq. ft. 3 14 10 1 0.5 1 2 3 pH 9.0 8.3 8.3 8.3 8.3 8.3 8.3 8.3

1 Fann reading, Fann. Y Apparent viscosity.

TABLE 7-B Cross-linking agent of the present invention, p.p.b.

FIR A/V F/R A/V F/R AIV F/R A/V F/R A/V FIR A/V F/R AN 8 24 12 36 18 54 17 51 8 24 18 54 19 2 98 3 147 5. 5 269. 5 4 196 2. 5 122. 5 4 195 5 245 3 1. 5 147 2 196 5 490 3 294 2 195 3 294 4. 5 441 Initial gel, lb./100 sq. ft 3 3 11 8 5 plI 9.0 8.5 8.4 8.2 8.2 8 3 8 3 1 Farm reading, Fann. 1 Apparent viscosity, centipoises.

EXAMPLE VIII Additional tests were conducted and results evaluated perature before determining rheological properties using the Fann Viscometer as described earlier. Fann viscometer tests taken at room temperature were also conducted on portions of the samples after aging for 16 hours at 150 F., in order to determine the eifect of higher temperatures on rheological properties. All tests resulted in no chromium ion overtreatment characteristics. Each sample showed thickening at increased p.p.b. levels. In

addition, excellent shear thinning properties were also obtained. Increased temperatures did not affect shear thinning characteristics.

TABLE 8A.TESIS IN HARD WATER BEFORE AGING Polysaccheride, p.p.b.

Applicants cross-linking agent, p.p.b.

Apparent Apparent Apparent Apparent Apparent Apparent Fann viscosity Fann viscosity Fann viscosity Fann viscosity Fann viscosity Fann viscosity 1S 9 19 9. 6 30 15 29 14. 5 31. 5 15. 5 36 18 12 12 13 13 2O 20 20 20 22 22 25 10 15 11 16.5 17 25 5 17 25 5 18 27 21 31 5 7 21 8 24 12 36 13 39 14 42 16 48 3 147 4 196 5 245 6 294 6 294 21 1020 3 2 5 245 3 294 4 392 6 588 5 490 16 1568 Initial gel, lb./l00 sq. ft. 9 8 8 12 10 12 pH 9.0 9.0 90 9.0 9.0

TABLE 8-B.TESTS IN HARD WATER AFTER AGING Polysaccharide, p.p.b.

Applicants cross-linking agent, p.p.b.

Apparent Apparent Apparent Apparent Apparent Apparent Fann viscosity Fann viscosity Farm viscosity Fann viscosity Fann viscosity Faun viscosity 14 7 21 10. 29 14. 5 25. 5 12. 75 31 15. 5 40 9. 5 9. 5 14. 5 14. 5 17 17 18 18 21 21 28 28 7. 5 11. 12 18 14 21 15 22.5 17 25. 5 22.5 33. 75 5 15 8 24 9. 5 28. 5 10. 5 31. 5 11. 5 34. 5 16 48 1 49 2. 5 122.5 3 147 3. 5 171. 5 3. 5 171.5 6.5 318. 5 3... 1 98 2 196 2. 5 245 2. 5 248 3 294 5 490 Initial gel, lb./100 sq. ft.- 1.5 3 3. 5 4 4 6 pH 7. 8 8. 0 8. 1 7. 8 8. 0 8. 0

TABLE 8C.TESTS IN SYNTHETIC SEAWATER BEFORE AGING Polysaccharide, p.p.b.

Applicants cross-linking agent, p.p.b.

Apparent Apparent Apparent Apparent Ap arent A arent Fann viscosity Fann viscosity Fann viscosity Fann viscosity Fann vis msity Fann v i s cosity TABLE 8-D.TESIS IN SYNTHETIC SEAWATER AFTER AGING Polysaccharide, p.p.b.

Applicants cross-linking agent, p.p.b.

Apparent Apparent Apparent Apparent Apparent Apparent Faun viscosity Fann viscosity Fann viscosity Fann viscosity Faun viscosity Fann viscosity 16 8 15 7. 5 18 9 23 11. 5 26 13 28 14 10.5 10.5 9 9 11 11 16 16 16 16 18 18 8 12 6 9 8 12 13 19. 5 12 18 13 19. 5 5. 5 16. 5 4 12 5 15 9 27 8 24 9 27 1. 5 73. 5 1 49 2 98 3 147 2. 5 122. 5 3 147 3, 1. 6 147 1 98 1- 5 147 2 19a 2 196 2, 5 245 Initial gel, lb./100 sq. ft. 2 1 2 4. 5 5 3 DH 7. 9 8. 1 8. 1 7. 9 s. 0 8. 0

EXAMPLE 1X Contrary to the conventional practice of drilling with An oil well was drilled in Reeves County, Tex., utilizing clayey suspensions, no bentonites or clays of any kind an aqueous drilling fluid contijlifling the macromolficu'lal' 50 were used to compose or treat the circulating fluid at any polysaccharide material cross-linked w1th the cross-lmkmg time prior to or during the course of drilling agetnt 8 the fw ggi gg 2 32 32 31: 5; i 8 The polysaccharide material was added at the rate of wa erase sys e about 11,500 feet had been reached. This system was then ten minutes Per Sack whlle the crss 1mkmg ag ent was pumped out of the well and the drilling fluid containing addefl at the rate of 16 Sacks P? 20 f- Sodlum the cross-linked macromolecular polysaccharide material drOXlde Was added evfiry 30 mlnlltes t0 adlust the P 10 was thereafter circulated during further drilling. The 8.0. The total mixing time was a little over two hours. drilling fluid consisted of the following materials which Samples of this drilling fluid were taken at various were blended 111 barrels of brme water: drilling depths from the flow line and the mud pit and M 1 l 1 h mat were tested as in previous examples for shear thinning zi sg i g g fig ysacc an e e 1 3 8 characteristics. It was found that the drilling fluid showed Sodium hydroxide nu- 375 excellent rheological properties for maximum penetration Biodegradation preventative .1 rate, as shown in the following table.

TABLE 9 Depths 11,490 ft 11,960 ft. 12,923 it. 13,357 ft. 13,928 ft. 14,974 ft.

F/R A/V F/R A/VI F/R 1 AN F/R 1 AN: F/R 1 i i/V F/R l A/V I 26 13 44 22 45 22. 5 35 17. 5 38 19 56 28 19 19 32 32 31 31 22 22 28 28 a9 a9 16 24 26 a9 25 a7. 5 17 25. 5 2a 34. 5 33 49. 5 12 36 19 57 17 51 11 33 18 54 29 78 4 196 5 25s 5 25s 4 19s 9 441 13 637 a 294 3 294 5 490 3 294 9 882 9 882 1 Farm reading, Fann. 1 Apparent viscosity, centipoises.

The ratio of cross-linking agent to macromolecular polysaccharide material can vary considerably depending on the selected industrial use and the particular environments and circumstances surrounding such use without encountering any metal ion overtreatment effect. For example, when using the cross-linked material of this invention in aqueous drilling fluids, formation characteristics, bore hole properties, drilling depth, contaminants, temperatures and pressures encountered, and drilling fluid weight will influence the determination of quantities of cross-linking agent and macromolecular polysaccharide material to be utilized in order to achieve the desired eflect. Because of this it is impossible to specifically state nominal ratios under all environments. Those skilled in the art of drilling will be able to easily determine needed ratios by testing samples obtained from the bore hole, checking formation characteristics, and by otherwise determining the rheological and other properties that will be required. Nevertheless, it can be stated that, under most drilling conditions, in order to obtain satisfactory shear thinning drilling fluid properties resulting from crosslinking the macromolecular polysaccharide material with the cross-linking agent of the present invention, a 4-to-1 cross-linking agent-to-polysaccharide ratio can be effectively utilized. When utilized in aqueous drilling fluids, our cross-linking agent has been found readily adaptable to all drilling environments, being eifective in fresh water, salt solutions, and in brines, at cross-linking agent-to-polysaccharide ratios as low as l-to-l and as high as 24-to-l.

It is important to note that, while cross-linking agents utilized in the prior art are sometimes able to produce cross-linked polysaccharide solutions having satisfactory rheological characteristics at p.p.b. levels which are somewhat lower than those suggested when using the crosslinking agent of the present invention, these characteristics are extremely difiicult to control. A minor miscalculation in p.p.b. concentration for these prior art cross-linking materials will often result in drastic metal ion overtreatment efiects which, in turn, drastically affect rheological characteristics. It is often desirable to utilize increased p.p.b. levels of a cross-linking agent for reasons which are secondary to rheology. For example, when utilizing a cross-linking agent in drilling fluids, the material may also serve the ofiice of bore hole stabilizer and filtration control agent. Under many drilling environments these functions cannot be efiectively accomplished at p.p.b. levels of .5 to 1.0. Thus, although satisfactory, though uncontrolled, rheology may be achieved utilizing prior art crosslinking agents at these low p.p.b. levels, other drilling fluid functions cannot be achieved. The discovery of the crosslinking agent of the present invention enables controlled rheology at increased p.p.b. levels, permitting sufiicient material to be added for bore hole stabilization, etc.

Although the invention has been described in terms of specified embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.

What we claim is:

1. The product produced by the process of:

(A) Dissolving in an aqueous solution a bacterially modified carbohydrate produced by the action of bacteria of the genus Xanthomonas on a carbohydrate selected from the class consisting of exudate gums, seaweed gums, seed gums, starch, cellulose and glucose;

(B) Adding to said solution a chelate cross-linking agent consisting essentially of (1) a tannin selected from the class consisting of wattle extract and quebracho and (2) chromium sulfate of one-third basicity or less, the ratio of said cross-linking agent to said modified carbohydrate being from about 1- to-1 to about 24-to-1, the chromium content of the said cross-linking agent being from between about 4% by weight to about 10% by weight;

(C) Adjusting the pH of the aqueous solution to between about 6 and about 7 to initiate cross-linking of the modified carbohydrate;

(D) Stirring the aqueous solution to prevent high pH localization; and

(E) Readjusting the pH of the aqueous solution up to about 11.0 to complete cross-linking of the modified carbohydrate.

2. The product of claim 1 wherein the said bacterially modified carbohydrate is produced by the action of the bacteria Xanthomonas campestris on said carbohydrate.

3. The product of claim 1 wherein the ratio of the cross-linking agent to the modified carbohydrate is about 4-to-1.

4. The product of claim 1 wherein the carbohydrate is glucose.

References Cited UNITED STATES PATENTS 3,074,927 1/1963 Saltman et al. 260-209 R 3,160,552 12/1964 Russell et al 260-209 R JOHNNIE R. BROWN, Primary Examiner US. Cl. X.R.

8-62, 115.6; 2528.5 A; 260124, 210 R, 212, 233.3, 4385 R 

